Haze is fog and haze is smog

Haze often veils hill and dale in late spring and early summer,
when the weather is variably cool and warm. The haze is sometimes
fog and sometimes smog, but few people can tell the difference.

Actually, fog and smog often coexist. Warm, dry air settles over
North County and Southwest Riverside County, frequently trapping
cool, moist air above the ocean to form fog.

The weather pattern is known as June Gloom at the coast but the
effects extend inland to the mountains.

The layering of warmer air over cooler air -- which
meteorologists call an inversion because air usually cools with
altitude -- also can hold pollutants near the ground to create
smog.

"Haze is a natural phenomenon," said Larry Riddle, a
climatologist at the Scripps Institution of Oceanography in La
Jolla. "Haze occurs all by itself. However, there is haze and there
is haze."

The meteorological definition of haze is fine dust or salt
particles in the air. But forecasters and laypersons alike use the
term to refer to reduced visibility due to moisture, pollution, or
anything else.

Riddle said he usually distinguishes manmade smog from natural
haze by color. The former is yellowish-brown, and the latter is
white, gray or even blue.

Another clue is weather conditions. Lung-irritating ozone, the
primary ingredient in smog, forms best in summer. Heat and sunlight
provide the energy for hydrocarbons and oxides of nitrogen -- which
provide smog with opacity and a distinct hue -- to react to make
ozone and other byproducts.

"Without actual air pollution measurements, it's hard to really
know generally if there's more of a brownish tint to the air and
things like that," said Bill Brick, senior meteorologist for the
Air Pollution Control District of San Diego County. "There can be
pollution and haze mixed together."

Brick said meteorologists lacked a code for smog in the old
days, so they used the codes for smoke and fog. However, the
expression originated in another hazy city a century ago from the
same combination of words.

Air pollution in London at the time took shape as a mixture of
smoke and fog. The famous London fogs were partly due to water
beading on particles in smoke emitted from homes and factories. In
the '50s, an inversion trapped dense smog long enough to kill
thousands of people.

In recent decades, many countries have taken steps to control
air pollution. Smog now results mostly from automobile exhaust. In
the United States, low-emission cars have reduced smog levels
despite growing numbers of vehicles.

"It's not as bad as it was 20 years ago," said Stan Wasowski, a
forecaster at the San Diego regional center of the National Weather
Service. "They've cleaned most of it."

San Diego County exceeded the federal one-hour ozone standard 87
times in 1980, Brick said, compared to once in the past three
years. But the county has yet to meet the stricter state standards
or the federal eight-hour ozone standard.

Brick said the county broke the federal standard for the average
ozone level over an hour when temperatures soared on May 8. The
ozone levels exceeded the standard at the monitoring site in
Alpine, which often sits in the inversion layer -- the boundary
where cool air meets warm air -- in the midst of the worst
smog.